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It remains largely unclear how thymocytes translate relative differences in T cell receptor (TCR) signal strength into distinct developmental programs that drive the cell fate decisions towards conventional (Tconv) or regulatory T cells (Treg). Following TCR activation, intracellular calcium (Ca2+) is the most important second messenger, for which the potassium channel K2P18.1 is a relevant regulator. Here, we identify K2P18.1 as a central translator of the TCR signal into the thymus-derived Treg (tTreg) selection process. TCR signal was coupled to NF-κB-mediated K2P18.1 upregulation in tTreg progenitors. K2P18.1 provided the driving force for sustained Ca2+ influx that facilitated NF-κB- and NFAT-dependent expression of FoxP3, the master transcription factor for Treg development and function. Loss of K2P18.1 ion-current function induced a mild lymphoproliferative phenotype in mice, with reduced Treg numbers that led to aggravated experimental autoimmune encephalomyelitis, while a gain-of-function mutation in K2P18.1 resulted in increased Treg numbers in mice. Our findings in human thymus, recent thymic emigrants and multiple sclerosis patients with a dominant-negative missense K2P18.1 variant that is associated with poor clinical outcomes indicate that K2P18.1 also plays a role in human Treg development. Pharmacological modulation of K2P18.1 specifically modulated Treg numbers in vitro and in vivo. Finally, we identified nitroxoline as a K2P18.1 activator that led to rapid and reversible Treg increase in patients with urinary tract infections. Conclusively, our findings reveal how K2P18.1 translates TCR signals into thymic T cell fate decisions and Treg development, and provide a basis for the therapeutic utilization of Treg in several human disorders.

Dimethyl fumarate, an approved treatment for relapsing-remitting multiple sclerosis, exerts pleiotropic effects on immune cells as well as CNS resident cells. Here, we show that dimethyl fumarate exerts a profound alteration of the metabolic profile of human CD4+ as well as CD8+ T cells and restricts their antioxidative capacities by decreasing intracellular levels of the reactive oxygen species scavenger glutathione. This causes an increase in mitochondrial reactive oxygen species levels accompanied by an enhanced mitochondrial stress response, ultimately leading to impaired mitochondrial function. Enhanced mitochondrial reactive oxygen species levels not only result in enhanced T-cell apoptosis in vitro as well as in dimethyl fumarate-treated patients, but are key for the well-known immunomodulatory effects of dimethyl fumarate both in vitro and in an animal model of multiple sclerosis, i.e. experimental autoimmune encephalomyelitis. Indeed, dimethyl fumarate immune-modulatory effects on T cells were completely abrogated by pharmacological interference of mitochondrial reactive oxygen species production. These data shed new light on dimethyl fumarate as bona fide immune-metabolic drug that targets the intracellular stress response in activated T cells, thereby restricting mitochondrial function and energetic capacity, providing novel insight into the role of oxidative stress in modulating cellular immune responses and T cell-mediated autoimmunity.

A close interaction between gut immune responses and distant organ-specific autoimmunity including the CNS in multiple sclerosis has been established in recent years. This so-called gut–CNS axis can be shaped by dietary factors, either directly or via indirect modulation of the gut microbiome and its metabolites. Here, we report that dietary supplementation with conjugated linoleic acid, a mixture of linoleic acid isomers, ameliorates CNS autoimmunity in a spontaneous mouse model of multiple sclerosis, accompanied by an attenuation of intestinal barrier dysfunction and inflammation as well as an increase in intestinal myeloid-derived suppressor-like cells. Protective effects of dietary supplementation with conjugated linoleic acid were not abrogated upon microbiota eradication, indicating that the microbiome is dispensable for these conjugated linoleic acid-mediated effects. Instead, we observed a range of direct anti-inflammatory effects of conjugated linoleic acid on murine myeloid cells including an enhanced IL10 production and the capacity to suppress T-cell proliferation. Finally, in a human pilot study in patients with multiple sclerosis (n = 15, under first-line disease-modifying treatment), dietary conjugated linoleic acid-supplementation for 6 months significantly enhanced the anti-inflammatory profiles as well as functional signatures of circulating myeloid cells. Together, our results identify conjugated linoleic acid as a potent modulator of the gut–CNS axis by targeting myeloid cells in the intestine, which in turn control encephalitogenic T-cell responses., Fleck et al. report that dietary supplementation with conjugated linoleic acid elicits anti-inflammatory and suppressive myeloid cell responses in the intestine, resulting in amelioration of CNS autoimmunity in mice and a beneficial modulation of myeloid cell responses in patients with relapsing-remitting multiple sclerosis.

Background The nuclear receptor farnesoid-X-receptor (FXR; NR1H4) is expressed not only in the liver, gut, kidney and adipose tissue but also in the immune cells. FXR has been shown to confer protection in several animal models of inflammation, including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). FXR agonists are currently tested in clinical trials for treatment of human metabolic diseases. The beneficial effect of FXR agonists in EAE suggests that FXR might represent a potential target in inflammatory-demyelinating CNS diseases, such as MS. In MS, oligodendrocytes not only undergo cell death but also contribute to remyelination. This repair mechanism is impaired due to a differentiation block of oligodendroglial progenitor cells. Activation of other nuclear receptors that heterodimerize with FXR promote oligodendroglial differentiation. Therefore, we wanted to address the functional relevance of FXR for glial cells, especially for oligodendroglial differentiation. Methods We isolated primary murine oligodendrocytes from FXR-deficient (FXR Ko) and wild-type (WT) mice and determined the effect of FXR deficiency and activation on oligodendroglial differentiation by analysing markers of oligodendroglial progenitor cells (OPCs) and mature oligodendrocytes (OLs) using qRT-PCR and immunocytochemistry. Additionally, we determined whether FXR activation modulates the pro-inflammatory profile of astrocytes or microglia and whether this may subsequently modulate oligodendroglial differentiation. These in vitro studies were complemented by histological analyses of oligodendrocytes in FXR Ko mice. Results FXR is expressed by OPCs and mature oligodendrocytes. However, lack of FXR did not affect oligodendroglial differentiation in vitro or in vivo. Furthermore, activation of FXR using the synthetic agonist GW4064 did not affect oligodendroglial differentiation, remyelination in an ex vivo model or the expression of pro-inflammatory molecules in astrocytes or microglia. Concordantly, no effects of supernatants from macrophages cultured in the presence of GW4064 were observed regarding a possible indirect impact on oligodendroglial differentiation. Conclusions Our data suggest that FXR is dispensable for oligodendroglial differentiation and that FXR agonists, such as GW4064, represent a potential therapeutic approach for MS which specifically targets peripheral immune cells including macrophages but not brain-resident cells, such as oligodendrocytes, astrocytes or microglia. Electronic supplementary material The online version of this article (doi:10.1186/s12974-017-0833-6) contains supplementary material, which is available to authorized users.

International audience; Interference with immune cell proliferation represents a successful treatment strategy in T cell-mediated autoimmune diseases such as rheumatoid arthritis and multiple sclerosis (MS). One prominent example is pharmacological inhibition of dihydroorotate dehydrogenase (DHODH), which mediates de novo pyrimidine synthesis in actively proliferating T and B lymphocytes. Within the TERIDYNAMIC clinical study, we observed that the DHODH inhibitor teriflunomide caused selective changes in T cell subset composition and T cell receptor repertoire diversity in patients with relapsing-remitting MS (RRMS). In a preclinical antigen-specific setup, DHODH inhibition preferentially suppressed the proliferation of high-affinity T cells. Mechanistically, DHODH inhibition interferes with oxidative phosphorylation (OXPHOS) and aerobic glycolysis in activated T cells via functional inhibition of complex III of the respiratory chain. The affinity-dependent effects of DHODH inhibition were closely linked to differences in T cell metabolism. High-affinity T cells preferentially use OXPHOS during early activation, which explains their increased susceptibility toward DHODH inhibition. In a mouse model of MS, DHODH inhibitory treatment resulted in preferential inhibition of high-affinity autoreactive T cell clones. Compared to T cells from healthy controls, T cells from patients with RRMS exhibited increased OXPHOS and glycolysis, which were reduced with teriflunomide treatment. Together, these data point to a mechanism of action where DHODH inhibition corrects metabolic disturbances in T cells, which primarily affects profoundly metabolically active high-affinity T cell clones. Hence, DHODH inhibition may promote recovery of an altered T cell receptor repertoire in autoimmunity.

Sodium chloride promotes vascular fibrosis, arterial hypertension, pro-inflammatory immune cell polarization and endothelial dysfunction, all of which might influence outcomes following stroke. But despite enormous translational relevance, the functional importance of sodium chloride in the pathophysiology of acute ischemic stroke is still unclear. In the current study, we show that high-salt diet leads to significantly worse functional outcomes, increased infarct volumes, and a loss of astrocytes and cortical neurons in acute ischemic stroke. While analyzing the underlying pathologic processes, we identified the migrasome as a novel, sodium chloride-driven pathomechanism in acute ischemic stroke. The migrasome was previously described in vitro as a migrating organelle, which incorporates and dispatches cytosol of surrounding cells and plays a role in intercellular signaling, whereas a pathophysiological meaning has not been elaborated. We here confirm previously reported characteristics of the migrasome in vivo. Immunohistochemistry, electron microscopy and proteomic analyses further demonstrate that the migrasome incorporates and dispatches cytosol of surrounding neurons following stroke. The clinical relevance of these findings is emphasized by neuropathological examinations, which detected migrasome formation in infarcted brain parenchyma of human stroke patients. In summary, we demonstrate that high-salt diet aggravates stroke outcomes, and we characterize the migrasome as a novel mechanism in acute stroke pathophysiology.

The increasing incidence in Multiple Sclerosis (MS) during the last decades in industrialized countries might be linked to a change in dietary habits. Nowadays, enhanced salt content is an important characteristic of Western diet and increased dietary salt (NaCl) intake promotes pathogenic T cell responses contributing to central nervous system (CNS) autoimmunity. Given the importance of macrophage responses for CNS disease propagation, we addressed the influence of salt consumption on macrophage responses in CNS autoimmunity. We observed that EAE-diseased mice receiving a NaCl-high diet showed strongly enhanced macrophage infiltration and activation within the CNS accompanied by disease aggravation during the effector phase of EAE. NaCl treatment of macrophages elicited a strong pro-inflammatory phenotype characterized by enhanced pro-inflammatory cytokine production, increased expression of immune-stimulatory molecules, and an antigen-independent boost of T cell proliferation. This NaCl-induced pro-inflammatory macrophage phenotype was accompanied by increased activation of NF-kB and MAPK signaling pathways. The pathogenic relevance of NaCl-conditioned macrophages is illustrated by the finding that transfer into EAE-diseased animals resulted in significant disease aggravation compared to untreated macrophages. Importantly, also in human monocytes, NaCl promoted a pro-inflammatory phenotype that enhanced human T cell proliferation. Taken together, high dietary salt intake promotes pro-inflammatory macrophages that aggravate CNS autoimmunity. Together with other studies, these results underline the need to further determine the relevance of increased dietary salt intake for MS disease severity.

T cells critically depend on reprogramming of metabolic signatures to meet the bioenergetic demands during activation and clonal expansion. Here we identify the transcription factor Nur77 as a cell-intrinsic modulator of T cell activation. Nur77-deficient T cells are highly proliferative, and lack of Nur77 is associated with enhanced T cell activation and increased susceptibility for T cell-mediated inflammatory diseases, such as CNS autoimmunity, allergic contact dermatitis and collagen-induced arthritis. Importantly, Nur77 serves as key regulator of energy metabolism in T cells, restricting mitochondrial respiration and glycolysis and controlling switching between different energy pathways. Transcriptional network analysis revealed that Nur77 modulates the expression of metabolic genes, most likely in close interaction with other transcription factors, especially estrogen-related receptor α. In summary, we identify Nur77 as a transcriptional regulator of T cell metabolism, which elevates the threshold for T cell activation and confers protection in different T cell-mediated inflammatory diseases.

In addition to their well known function in astrocyte coupling, gap junction forming connexins are also important for cell proliferation, migration and differentiation during brain development. The aim of this study was to determine whether loss of the main astrocytic connexins, connexin 43 (Cx43) or connexin 30 (Cx30), influences various stages of adult hippocampal neurogenesis. To that end, mice with a conditional Cx43 deletion in astrocytes and mice with a conventional knockout of Cx30 were used. We assessed cell proliferation based on Ki67-immunoreactive cell number and cell survival based on BrdU-immunoreactive cell number in the subgranular zone (SGZ) and the granular cell layer (GCL) of the dentate gyrus. The neuronal phenotype of surviving cells was analyzed following immunofluorescent co-localization of BrdU-positive cells with the neuronal markers doublecortin (DCX) and neuronal nuclear antigen (NeuN). Ablation of Cx43 in astrocytes significantly diminished proliferation and reduced the overall survival of newborn cells. In contrast, knockout of Cx30 showed a tendency towards increased proliferation and significantly enhanced the overall survival of newborn cells. The differentiation of surviving cells into neurons is unaffected following Cx43 or Cx30 knockout. Our data reveal that Cx43 promotes the survival of newborn neurons in the adult mouse hippocampus whereas Cx30 restricts their survival.

Innate immune responses by myeloid cells decisively contribute to perpetuation of central nervous system (CNS) autoimmunity and their pharmacologic modulation represents a promising strategy to prevent disease progression in Multiple Sclerosis (MS). Based on our observation that peripheral immune cells from relapsing-remitting and primary progressive MS patients exhibited strongly decreased levels of the bile acid receptor FXR (farnesoid-X-receptor, NR1H4), we evaluated its potential relevance as therapeutic target for control of established CNS autoimmunity. Pharmacological FXR activation promoted generation of anti-inflammatory macrophages characterized by arginase-1, increased IL-10 production, and suppression of T cell responses. In mice, FXR activation ameliorated CNS autoimmunity in an IL-10-dependent fashion and even suppressed advanced clinical disease upon therapeutic administration. In analogy to rodents, pharmacological FXR activation in human monocytes from healthy controls and MS patients induced an anti-inflammatory phenotype with suppressive properties including control of effector T cell proliferation. We therefore, propose an important role of FXR in control of T cell-mediated autoimmunity by promoting anti-inflammatory macrophage responses.

Age-induced neuroinflammation could be a contributing factor to the restricted neurogenesis in aged mice. Indomethacin, a common non-steroidal anti-inflammatory drug, has been demonstrated to partially restore neurogenesis under pathophysiological inflammation-associated conditions in adult C57BL/6 mice. This study investigated whether indomethacin is able to decrease age-related neuroinflammation in the hippocampus (24-month-old mice) and thereby stimulate neurogenesis. During hippocampal aging, the transcript expression of pro-inflammatory cytokines (Tnfα, Il-1α, Il-1β), the chemokine Mip-1α, and markers for activated astrocytes (Gfap, Lcn2, but not Vim and Serpina3n) and microglia (Iba1, F4/80, Cd68, Cd86) significantly increased. Treatment with indomethacin significantly decreased COX-1 and COX-2 transcript expression. Of the age-related inflammatory mediators, only Gfap and Iba1 were affected by indomethacin treatment in the hippocampus, with a significantly reduced transcript expression being detected for both markers. Neurogenesis was unaffected by indomethacin. Thus, our data reveal that administration of indomethacin to aged mice is not able to effectively decrease neuroinflammation and promote neurogenesis.